Rh-Catalyzed Oxidative Coupling between Primary and Secondary Benzamides and Alkynes: Synthesis of Polycyclic Amides

Song, Guoyong; Chen, Dan; Pan, Cheng‐Ling; Crabtree, Robert H.; Li, Xingwei

doi:10.1021/jo101596d

Cited by 308 publications

(99 citation statements)

References 42 publications

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“…(1)], [6] thus resulting in the generation of undesired waste. Recently, Fagnou et al reported an oxidizing-directing-group strategy [7] for the rhodium-catalyzed synthesis of isoquinolones by intermolecular CÀH activation of N-methoxy/pivaloyloxy benzamides and alkynes [Eq.…”

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confidence: 99%

“…The indolizidine structural motif forms the core of many natural products with pharmacological relevance, such as indolizidine [1] and phenanthroindolizidine [2] alkaloids (septicine (1), antofine (2), and tylophorine (3)), camptothecin (4, CPT), [3] and aromathecin alkaloids [4] (rosettacin (5) and 22-hydroxyacuminatine (6)). While a number of synthetic methods for the construction of these scaffolds have been reported, [1][2][3][4] the development of conceptually different synthetic approaches is still of great interest.…”

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confidence: 99%

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Rhodium(III)‐Catalyzed Intramolecular Annulation through CH Activation: Total Synthesis of (±)‐Antofine, (±)‐Septicine, (±)‐Tylophorine, and Rosettacin

2012

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The indolizidine structural motif forms the core of many natural products with pharmacological relevance, such as indolizidine [1] and phenanthroindolizidine [2] alkaloids (septicine (1), antofine (2), and tylophorine (3)), camptothecin (4, CPT), [3] and aromathecin alkaloids [4] (rosettacin (5) and 22-hydroxyacuminatine (6)). While a number of synthetic methods for the construction of these scaffolds have been reported, [1][2][3][4] the development of conceptually different synthetic approaches is still of great interest.The rhodium(III)-catalyzed oxidative CÀH activation has received significant interest in recent years because of its high efficiency, selectivity, and functional-group tolerance.[5] Generally, these reactions require stoichiometric amounts of external oxidants [Eq. (1)], [6] thus resulting in the generation of undesired waste. Recently, Fagnou et al. reported an oxidizing-directing-group strategy [7] for the rhodium-catalyzed synthesis of isoquinolones by intermolecular CÀH activation of N-methoxy/pivaloyloxy benzamides and alkynes [Eq. (2); Piv = pivaloyl], [8] which not only obviates the need for an external oxidant, but also increases the reactivity and selectivity under mild conditions. During our investigation of the reactivity of a-oximino carbenoids, [9] we observed facile intramolecular N À O insertion of oxime ether moieties, which results in the formation of 2-alkoxy/aryloxy-2H-azirines.[10]The cleavage of the N À O bond plays an important role in Fagnous rhodium-catalyzed intermolecular CÀH activation of N-methoxy/pivaloyloxy benzamides and in our NÀO insertion of a-oximino carbenes. Based on this observation, we became interested in the intramolecular reaction of alkyne-tethered hydroxamic esters [Eq. (3)]. The successful development of this reaction would lead to a general and facile synthesis of hydroxyalkyl-substituted isoquinolone/2-pyridone derivatives, which could be readily transformed into indolizidine scaffolds. Herein, we wish to report these results, and the total synthesis of (AE)-antofine, (AE)-septicine, (AE)-tylophorine, and rosettacin based on rhodium(III)-catalyzed C À H bond functionalization as the key step.Our synthetic attempts began with the reaction of 7 a by employing Fagnous intermolecular reaction conditions [7] (Table 1, entries 1 and 2). We found that treatment of 7 a with [(Cp*RhCl 2 ) 2 ] (2.5 mol %) and CsOAc (30 mol %) in MeOH at 60 8C gave isoquinolones 8 a and 8 a' (29:1) in 98 % yield in 0.2 hours (Table 1, entry 1). Similar results were obtained with a reduced catalyst loading (0.5 mol %) and reaction temperature, however, a longer reaction time was required in this case (12 h; Table 1, entry 2). Improved

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Rhodium(III)‐Catalyzed Intramolecular Annulation through CH Activation: Total Synthesis of (±)‐Antofine, (±)‐Septicine, (±)‐Tylophorine, and Rosettacin

2012

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“…4 The proposed mechanism for the Co(III)-catalyzed coupling of alkynes and amides to afford isoquinolones is closely related to the analogous Rh(III)-catalyzed reaction (Fig. 2) [55][56][57][58]. Coordination of the amide and quinoline moieties generates intermediate 8 that can undergo C-H activation, presumably via a CMD mechanism to generate metallacycle 9.…”

Section: Cobalt Catalysismentioning

confidence: 98%

High-Valent Co(III)- and Ni(II)-Catalyzed C–H Activation

Hyster

2014

Catal Lett

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The past two decades have witnessed explosive growth in the field of catalytic C-H activation. While this reactivity is typically associated with second-and thirdrow transition metals, first-row transition metals are also capable of catalyzing these reactions. C-H activation reactions can be further divided into ones where the C-H activation occurs with a low-valent metal and those where the activation occurs with a high-valent metal. This review will summarize advances in the area of high-valent Co(III)-and Ni(II)-catalyzed C-H activation with particular emphasis paid to how these catalysts compare their secondand third-row congeners.

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“…(5.57) and (5.58)). Both N-alkyl and N-aryl secondary benzamides could be employed, whereas primary benzamides reacted differently, and two alkyne units were oxidatively incorporated to give tricyclic products such as 60 [33]. The reaction was further extended to the annulation of N-pivaloxybenzamide with terminal alkynes to give 3-substituted isoquinolones 61 with good regioselectivity under mild conditions (Eq.…”

Section: Synthesis Of Isoquinolones and Related Derivativesmentioning

confidence: 99%